Just think of filling a bath when you forgot to put the plug in
At present, confirmed cases in the UK are declining; by specimen date in England, they fell by 29% in the week up to 24 July. In contrast, the Office for National Statistics (ONS) estimates that over the same period the proportion of the population in England infected with SARS-CoV-2 continued to rise, to around 1 in 60. Is there a conflict between these trends?
The measures are somewhat different: testing data provides new recorded infections (the incidence); Public Health England counts some positives from rapid tests, as well as standard PCR tests. The ONS results are based on its large infection survey: a nationally representative sample is repeatedly PCR-tested for the virus and so estimates how many people would currently test positive (the positivity).